Electric coupling system



May 16, 1933. Q TRUBE 1,908,934

ELECTRIC COUPLING SYSTEM Original Filed May 14, 1930 j z: L I I'm i A BYABM 77M 2 ATTORNEYS Patented May 16, 1933 UNITED STATES PATENT OFFICECARL E. TRUIBE, DECEASED, LATE OF OSSINING, NEW YORK, BY SARAH M. TRUBE,

ADMINISTRATRIX, 0F OSSINING, NEW YORK, ASSTGNOR T0 HAZELTINE CORPORA-TION, .A. CORPORA'IION' OF DELAWARE i ELECTRIC COUPLING SYSTHE Originalapplication filed. May 14, 1930, Serial No.

Serial No. 522,344.

This invention relates to electric coupling systems especially adaptedfor use with radio-frequency vacuum or thermionic tube amplifiers, andmore particularly tocircuit arrangements which operate most effectivelyover a relatively wide range in frequency. The coupling systems are soarranged as to give a voltage ratio that varies automatically with thefrequency. The variation in voltage ratio is accomplished in a primarycircuit which includes a fixed self-inductance effectively in parallelwith one or more fixed capacities external to the main resonant circuitand which may be electrically'ls'olated from the main resonant circuit.The 'primary circuit is resonant at a frequency lower (but preferablynot greatly lower) than the lowest frequency within the range of thecoupling system. Coupling systems answering this description aredescribed generally in application for U. S. Letters Patent, Serial No.292,739, patented June 10, 1930, No. 1,763,380, and in a divisionthereof, Serial No. 452,464, filed May 14, 1930, patented March 31,1931', No. 1,798,962. The present application is in turn a division ofthe mentioned application Serial No. 452,464.

The voltage ratio in an inter-tube coupling system affects the degree ofamplification, the stability and the selectivity. At each frequencythere is a particular who of output voltage to input voltage that Wlllgive the best compromise design. This ratio varies rapidly with thefrequency, being relatively high at high frequencies. This inventionprovides means for securing substantially the most desirable ratio atall frequencies without having any adjustable element except the tuningadjustment.

Referring to the drawing, Fig. 1 lllustrates a vacuum tube and anelectric coupling system embodying a simple form of this invention.

Fig. 2 illustrates a modification of Fig. 1 having an additional fixedcapacity.

Fig. 3 illustrates a modification of Fig. 2 in which a two-coiltransformer replaces an auto-transformer.

Fig. 4 illustrates a modification of Fig. 3

452,464, now Patent No. 1,798,962, dated March 31, Divided and thisapplication filed March 13, 1931.

by which direct voltage is removed from the fixed capacity.

The coupling system of Fig. 1 is tuned by a variable condenserCconnected across the primary coil L and the secondary coil L in series.Ordinarily L should have much .fewer turns than L so that ithere is ahigh step-up voltage ratio between them. The path through the primarycoil L from the plate of the vacuum tube to the filament includes alsothe fixed capacity G which is external to the main resonant circuit C LL In parallel with this path" is a second path including theself-inductance L the value of which is so chosen that its circuit(completed through C and L is resonant at a frequency lower, but notgreatly lower,

than the lowest frequency within the range of condenser G I The circuitof L being completed through 5 and L is thereby coupled to themainresonant circuit C L L so that part of the current of C and L will flowthrough C; and L this part of the current being limited mostly by thereactance of L Since the reactance of L varies directly with thefrequency while that of C varies inversely with the frequency, thevoltage across C will rapidly fall off relative to the voltage across Las the frequency rises. For a given output voltage E the voltage acrossL is very nearly independent of frequency, due to the electromagneticcoupling between L and Hence the voltage E between the plate or anodeand the filament or cathode, being the sum of the voltages of O and Lwill fall off relative to E as the frequency rises, but less rapidlythan the voltage across 0 alone. This is the condition'which is desiredand which results in the maintenanceof a high degree of stability overthe frequency range, together with high sensitivity and selectivity.

The operation of the circuit of Fig. 2 is essentially the same as that-of Fig. 1, but

here the circuit of L is completed through range of C lowest frequencywithin the The voltage ratio E /E is obtained from a double step-up,first between G and the combination of O and C and then between L and Land, with the resonant condition just given, this voltage ratio willautomatically vary with the frequency in the same manner as in Fig. 1.

Fig; 3 difi'ers from Fig. 2 only in that the primary coil L is notincluded in the main resonant circuit. Coil L should here have the samenumber of turns as in Fig. 2; while the secondary coil L should have thesame number of turns as L and L combined, in Fig. 2. The remainingrelations are the same as in Fig. 2. V

In Fig. 3 the direct voltage of the plate battery B exists acrosscondensers C and C which is disadvantageous in that these condensers maybreak down. This difficulty is obviated in Fig. 4 by connecting thelower terminals of condenser G and coil L to the lower, than the lowerterminal of coil L instead of to the common lead at the bottom of thediagram. This connection does not alfect the alternating-currentrelations of Fig. 4, which are identical with those of Fig. 3.

'What is claimed is 1. In a high-frequency system, a thermi onic tubehaving anode, cathode and control electrodes, an electric couplingsystem comprising a resonant circuit tunable throughout a range infrequency, and a second circuit including fixed inductance and capacityproportioned to produce resonance at a frequency below said tunablerange, said fixed capacity being external to said resonant circuit,andsaid fixed inductance being electromagnetically uncoupled fromsaidtunable circuit, a coupling impedance having a fixed voltage ratiorelative to said tunable circuit,

and a path through said coupling system between said anode and-cathodeincluding in series said coupling impedance and at least a. portion ofsaid fixed capacity, said coupling impedance being much smaller than athat of said portion of said fixed capacity throughout said rangeinfrequency, the elements of said coupling system being so proportionedthat the ratio of resonant voltage developed across said tunable circuitto an input voltage impressed between said cathode and controlelectrodes remains substantially constant as the tuning isvariedthroughout said frequency range.

2. In a high-frequency. system, a thermionic tube having anode, cathodeand control electrodes, an electric coupling system comprising aresonant secondary circuit tunable throughout a range in frequency, anda primary circuitincluding fixed inductance and capacity proportioned toproduce resonance below said tunable range, said fixed capacity beingexternal to said secondary circuit and including the auode-to-cathodecapacity of said tube, said fixed inductance being un coupledelectromagnetically from said secondary circuit, a coupling impedancehaving a fixed voltage ratio relative to said secondary circuit, and apath through said coupling system between saidanode and cathodeincluding in series said coupling impedance and a portion of said fixedcapacity, said coupling impedance being much smaller than that of saidportion of said fixed capacity throughout said range in frequency, theelements of said coupling system being so pro-- portioned that the ratioof resonant voltage developed across said secondary circuit to an inputvoltage impressed between said cathode and control electrodes remainssubstantially constant as the tuning is adjusted throughoutsaid'frequency range.

3. In a high-frequency system, a thermionic tube having anode, cathodeand control electrodes, an electric coupling system which comprises amain resonant circuit including as elements a secondary coil and acondenser at least one of which is adjustable to vary the tuningthroughout a range in frequency, a second circuit including fixedself-inductance effectively in parallel with fixed capacity externaltosaid main resonant, circuit, said self-inductance and fixed capacitylast mentioned being proportioned to produce resonance in said secondcircuit at a frequency lower than the lowest frequency within saidtunable range, a primary coil electromagnetically coupled to saidsecondary coil and a path through said coupling system between saidanode andcathode including in series said primary coil and at least aportion of said fixed capacity, said primary coil having much smallerreactance than said portion of said fixed'capacity throughout said rangein frequency, the elements of said coupling system being so proportionedthat the ratio of resonant voltage developed across said secondary coilto an input voltage impressed between said cathode and controlelectrodes remains substantially constant as the tuning is adjustedthroughout said frequency range.

4. A high-frequency coupling system having input terminals andcomprising a resonant circuit tunable'througho'ut a range in frequencyby adjustment of a single variable element, and a second circuitincluding fixed inductance and capacity proportioned to produceresonance at a frequency below' said tunable range, said fixed capacity.being external to said resonant circuit, and said fixed inductance beingelectromagnetically uncoupled from said tunable circuit, a couplingportion of said fixed capacity throughout said range in frequency, theaforementioned proportioning of elements in said coupling system beingsuch that there is developed in said tunable circuit a resonant voltagewhose ratio to the voltage impressed between said input terminalsautomatically rises with frequency as the tuning is Varied throughoutsaid frequency range by adjustment of said single variable element.

5. In a high-frequencysystem,athermionic tube having anode, cathode andcontrol electrodes, an electric coupling system comprising a resonantcircuit tunable throughout a range in frequency by adjustment of asingle variable element, and a second circuit including fixed inductanceand capacity proportioned to produce resonance at a frequency belowsaidtunable range, said fixed capacity being external to said resonantcircuit, and said fixed inductance being electromagnetically uncoupledfrom said tunable circuit, a coupling impedance having a fixed voltageratio relative to said tunable circuit, and a path through said couplingsystem between said anode and cathode including in series said couplingimpedance and at least a portion of said fixed capacity, said couplingimpedance having a much smaller reactance than said portion of saidfixed capacity throughout said range in frequency, the elements of saidcoupling system being so proportioned that the ratio of resonant Voltagedeveloped across said tunable circuit to an input voltage impressedbetween said cathode and control electrodes remains substantiallyconstant as the tuning is varied throughout said frequency range byadjustment of said single variable element.

6. In a high-frequency system, a thermionic tube having anode, cathodeand control electrodes, an electric coupling system which comprises amain resonant circuit including as elements a secondary coil and asingle variable condenser for adjusting the tuning throughout a range infrequency, a second circuit including fixed self-inductance effectivelyin parallel with fixed capacity external to said main resonant circuit,said fixed self-inductance and fixed capacity being proportioned toproduce resonance in said second circuitat a frequency lower than thelowest frequency within said tunable range, a coupling impedance havinga fixed voltage ratio relative to said main resonant circuit, and a paththrough said coupling system between said anode and cathode includ ingin series said'couplin impedance and at least a portion of said xedcapacity, said coupling impedance having a much smaller reactance thansaid portion of said fixed capacity throughout said range in frequency,the aforementioned proportioning of, elements in said coupling systembeing such that there is developed in said main resonant cir- SARAHv M.TRUBE, Administratriw 0f the Estate of Carl E.

Tru be, Deceased.

